Enantioselective synthesis of pyrrolidines substituted with flavones, and intermediates thereof

ABSTRACT

The present invention relates to an enantioselective synthesis of (+)-trans enantiomer of pyrrolidines substituted with flavones, represented by Formula 1 or salts thereof, which are inhibitors of cyclin dependant kinases and can be used for treatment of proliferative disorders such as cancer 
                         
wherein Ar has the meaning as indicated in the claims.

FIELD OF INVENTION

The present invention relates to an enantioselective synthesis of the(+)-trans enantiomer of pyrrolidines substituted with flavones,represented by the compounds of Formula 1 or salts thereof, which areinhibitors of cyclin dependant kinases and can be used for treatment ofproliferative disorders such as cancer.

BACKGROUND OF THE INVENTION

Cyclin dependent kinases (Cdks) are essential enzymes for the control ofcell cycle progression. Inhibitors of cyclin-dependent kinases areanticipated to possess therapeutic utility against a wide variety ofproliferative diseases, especially cancer. As a result of this, the CDKshave been targeted for drug discovery and a number of small moleculeinhibitors of CDKs have been identified and studied. Inhibitors ofCDK/cyclin complexes represented by the following general Formula 1;

wherein Ar is defined in the detailed description;have been described in PCT Patent Application No. PCT/IB2006/052002,which is incorporated herein by reference. These compounds exhibit goodselectivity and cytotoxicity against various proliferative cell lines.The novel compounds disclosed in the aforesaid patent application, havetwo chiral centers and hence, can exist as four enantiomers i.e.(+)-trans, (−)-trans, (+)-cis and (−)-cis. Chirality has acquiredincreasing importance for the pharmaceutical industry, as evidenced bythe fact that more than 80% of the drugs developed hitherto have chiralproperties. The various enantiomers may develop completely differenteffects in the body, so that only one of two or more enantiomeric formsadministered may be effective. In the case of the compounds of Formula1, it has been observed that only the (+)-trans enantiomers haveactivity while the (−)-trans enantiomers are inactive. An extensivestudy by the present inventors of the efficacy of the racemic compoundsof Formula 1 and their separate enantiomers has resulted in theapplicant's PCT Patent Application No. PCT/IB2006/052002. Administrationof the active (+)-trans enantiomer of any of the compounds representedby Formula 1, substantially free of its other isomers, would essentiallyenable a reduction in the dose of drug. Due to the importance of the(+)-trans enantiomers of the compounds represented by Formula 1 asinhibitors of cyclin dependant kinases, there exists a need to developan economical and efficient synthetic process for their production.

Applicant's PCT Patent Application No. PCT/IB2006/052002 describes aprocess for the preparation of the (+)-trans enantiomer of a pyrrolidinesubstituted with a flavone represented by the following Formula 1;

wherein Ar is defined in the detailed description.

The process as described in the PCT Patent Application No.PCT/IB2006/052002 involves resolution of an intermediate compound andsubsequent conversion of the resolved intermediate compound to thecompound represented by Formula 1. For instance,(+)-trans-2-(2-chlorophenyl)-5,7-dihydroxy-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-chromen-4-onewas prepared by resolution of an intermediate, namely(±)-trans-[1-methyl-3-(2,4,6-trimethoxy-phenyl)-pyrrolidin-2-yl]-methanol,and subsequent conversion of the (−)-trans isomer of the intermediate to(+)-trans-2-(2-chlorophenyl)-5,7-dihydroxy-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-chromen-4-one.The preparation of the (−)-trans-isomer of the intermediate involves thesteps of treating its racemate with a chiral auxiliary to obtain thecorresponding (+)- and (−)-trans diastereomeric salts followed byseparating the desired diastereomeric salt by crystallization andtreating it with a base to yield the desired (−)-trans enantiomer. Thisresolution method involves significant processing and also the use ofresolving agent renders the process costly. Partial recycling of theresolving agent is feasible but such recycling is costly as it requiresadditional processing and is also associated with waste generation. Theundesired enantiomer cannot be recycled and is discarded. The maximumtheoretical yield of the key intermediate obtained is just 50% on alaboratory scale synthesis due to loss of half of the racemate. Thisyield may be further reduced due to the need for high chiral purity(>95% enantiomeric excess). Thus, there is a clear need to develop analternative asymmetric synthesis which would provide the desired(+)-trans enantiomer in an efficient and more specific manner.

The object of this invention is to provide an alternative process forthe preparation of the (+)-trans enantiomer of the compounds representedby Formula 1, which is an enantioselective process. The process of thepresent invention allows efficient large-scale synthesis by overcomingthe drawbacks of the conventional resolution technique.

SUMMARY OF THE INVENTION

The present invention provides a novel process for the enantioselectivesynthesis of the (+)-trans enantiomer of a compound represented byFormula 1;

wherein Ar is defined in the detailed description.

The process of the present invention also involves the enantioselectivesynthesis of a compound of the following Formula A; which is the chiralprecursor of the compound of Formula 1;

The process of the present invention provides an enantioselectivesynthesis of the (+)-trans enantiomers of the compounds of Formula 1,which avoids the drawbacks of the aforementioned process.

The process of the present invention also has an additional advantage interms of cost and time as all the intermediates in the process arecrystalline and need no further purification.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is specifically directed to a process for theenantioselective synthesis of the (+)-trans enantiomer of a compoundrepresented by Formula 1;

wherein Ar is phenyl, which is unsubstituted or substituted by 1, 2, or3 identical or different substituents selected from: halogen, nitro,cyano, C₁-C₄-alkyl, fluoromethyl, difluoromethyl, trifluoromethyl,hydroxyl, C₁-C₄-alkoxy, carboxy, C₁-C₄-alkoxycarbonyl,C₁-C₄-alkylenehydroxyl, CONH₂, CONR₁R₂, SO₂NR₁R₂, cycloalkyl, NR₁R₂ andSR₃;wherein R₁ and R₂ are each independently selected from: hydrogen,C₁-C₄-alkyl, C₁-C₄-alkylcarbonyl and aryl, or R₁ and R₂, together withthe nitrogen atom to which they are bonded, form a 5- or 6-memberedring, which may optionally contain at least one additional heteroatom;andR₃ is selected from hydrogen, C₁-C₄-alkyl, aryl and SR₄, wherein R₄ isC₁-C₄-alkyl or aryl.

For the purpose of the disclosure, listed below are definitions ofvarious terms used to describe the compounds of the present invention.These definitions apply to the terms as they are used throughout thespecification (unless they are otherwise limited in specific instances)either individually or as part of a larger group. They should not beinterpreted in the literal sense. They are not general definitions andare relevant only for this application.

The term “alkyl” refers to the radical of saturated aliphatic groups,including straight-chain alkyl groups and branched-chain alkyl groups.Furthermore, unless stated otherwise, the term “alkyl” includesunsubstituted alkyl groups as well as alkyl groups, which aresubstituted by one or more different substituents. Examples of alkylresidues containing from 1 to 20 carbon atoms are: methyl, ethyl,propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl,dodecyl, tetradecyl, hexadecyl, octadecyl and eicosyl, the n-isomers ofall these residues, isopropyl, isobutyl, 1-methylbutyl, isopentyl,neopentyl, 2,2-dimethylbutyl, 2-methylpentyl, 3-methylpentyl, isohexyl,2,3,4-trimethylhexyl, isodecyl, sec-butyl, or t-butyl.

The term “cycloalkyl” refers to a non-aromatic mono or multicyclic ringsystem of about 3 to 7 carbon atoms which may be unsubstituted orsubstituted by one or more different substituents. Examples ofcycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl and the like.

The term “alkoxy” as used herein refers to an alkyl group, as definedabove, having an oxygen radical attached thereto. Representative alkoxylgroups include methoxy, ethoxy, propoxy, t-butoxy and the like.

The term “halogen” refers to chlorine, bromine, fluorine and iodine.

The term “heteroatom” refers to nitrogen, oxygen, sulphur andphosphorus.

The term “enantiomeric excess” refers to a difference between the amountof one enantiomer and the amount of the other enantiomer that is presentin the product mixture. Thus for example, enantiomeric excess of 96%refers to a product mixture having 98% of one enantiomer and 2% of theother enantiomer.

Where the stereochemistry is depicted in the structures it represents arelative rather than an absolute configuration.

In one embodiment of the present invention, there is provided a processfor the enantioselective synthesis of the compound,(−)-trans-(1-methyl-3-(2,4,6-trimethoxyphenyl)pyrrolidin-2-yl)methanolrepresented by the following Formula A;

(hereinafter referred to as compound A), or a pharmaceuticallyacceptable salt thereof,which process comprises the steps of:

-   -   (a) carrying out a stereospecific Michael addition of dimethyl        malonate to        (E)-methyl-2-nitro-3-(2,4,6-trimethoxyphenyl)acrylate in a        solvent in the presence of a catalyst complex, a base and a        molecular sieve, wherein the catalyst complex comprises a chiral        bis(oxazoline) ligand and a metal complex, to obtain        (+)-trimethyl 3-nitro-2-(2,4,6-trimethoxyphenyl)        propane-1,1,3-tricarboxylate represented by the following        Formula B;

-   -    (hereinafter referred to as compound B);    -   (b) treating compound B as obtained in step (a) with a reducing        agent in a suitable solvent to obtain (+)-dimethyl        5-oxo-3-(2,4,6-trimethoxyphenyl)-pyrrolidine-2,4-dicarboxylate        represented by the following Formula C;

-   -    (hereinafter referred to as compound C);    -   (c) treating compound C with sodium chloride in a solvent and        heating the resulting reaction mixture to a temperature in the        range of 120-170° C. to obtain        (+)-methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate        as a mixture of cis and trans isomers, represented by the        following Formula D;

-   -    (hereinafter referred to as compound D);    -   (d) reacting compound D with a methylating agent and a base        selected from: an alkaline metal hydride and an alkaline metal        carbonate, in a solvent, followed by subjecting the resulting        mixture of cis and trans compounds to alkaline hydrolysis with        an alkaline metal hydroxide in an alcohol with heating to a        temperature in the range of 50-100° C. to obtain        (−)-trans-1-methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)-pyrrolidine-2-carboxylic        acid, represented by the following Formula E;

-   -    (hereinafter referred to as compound E) as a single trans        isomer;    -   (e) treating compound E with a reducing agent in a solvent to        obtain the desired        (−)-trans-(1-methyl-3-(2,4,6-trimethoxyphenyl)pyrrolidin-2-yl)-methanol,        represented by Formula A.

In one embodiment, the present invention provides the use of compound A,as obtained by the novel process described, for the preparation of acompound represented by Formula 1.

According to another embodiment of the present invention, there isprovided a process for the preparation of the (+)-trans enantiomer of acompound represented by Formula 1;

wherein Ar is phenyl, which is unsubstituted or substituted by 1, 2, or3 identical or different substituents selected from: halogen, nitro,cyano, C₁-C₄-alkyl, fluoromethyl, difluoromethyl, trifluoromethyl,hydroxyl, C₁-C₄-alkoxy, carboxy, C₁-C₄-alkoxycarbonyl,C₁-C₄-alkylenehydroxyl, CONH₂, CONR₁R₂, SO₂NR₁, R₂, cycloalkyl, NR₁R₂and SR₃;wherein R₁ and R₂ are each independently selected from: hydrogen,C₁-C₄-alkyl, C₁-C₄-alkylcarbonyl and aryl, or R₁ and R₂, together withthe nitrogen atom to which they are bonded, form a 5- or 6-memberedring, which may optionally contain at least one additional heteroatom;andR₃ is selected from hydrogen, C₁-C₄-alkyl, aryl and SR₄, wherein R₄ isC₁-C₄-alkyl or aryl;or a pharmaceutically acceptable salt thereof;which process comprises:

-   -   (i) treating compound A (above) with acetic anhydride in the        presence of a catalyst to obtain (−)-trans-acetic acid        3-(3-acetyl-2-hydroxy-4,6-dimethoxy-phenyl)-1-methyl-pyrrolidin-2-yl        methyl ester represented by the following Formula F;

-   -    (hereinafter referred to as compound F);    -   (ii) treating compound F with an aqueous solution of an alkali        and raising the temperature of the reaction mixture to about        50° C. to obtain        (−)-trans-1-[2-hydroxy-3-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-4,6-dimethoxy-phenyl)-ethanone        represented by the following Formula G;

-   -    (hereinafter referred to as compound G);    -   (iii) reacting compound G with an ester of formula ArCOOCH₃        (wherein Ar is as defined in Formula 1) in presence of a base        and a suitable solvent under an atmosphere of nitrogen, followed        by acid catalyzed cyclisation to give the dimethoxy compound        represented by the following Formula 2;

-   -    (hereinafter referred to as compound 2);    -   (iv) subjecting compound 2 to demethylation by heating it with a        demethylating agent at a temperature in the range of 120-180° C.        to obtain the desired (+)-trans enantiomer of the compound        represented by Formula 1.

In the most preferred embodiment, the present invention provides aprocess for the enantioselective synthesis of(+)-trans-2-(2-chloro-phenyl)-5,7-dihydroxy-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-chromen-4-one,represented by the Formula 1A below, where in the compounds of generalFormula 1 the Ar group represents phenyl substituted with chlorine;

(hereinafter referred to as compound 1A), which process comprises:

-   -   (i) treating compound A with acetic anhydride in the presence of        a catalyst to obtain (−)-trans-acetic acid        3-(3-acetyl-2-hydroxy-4,6-dimethoxy-phenyl)-1-methyl-pyrrolidin-2-yl        methyl ester represented by the following Formula F;

-   -    (hereinafter referred to as compound F);    -   (ii) treating compound F with an aqueous solution of an alkali        and raising the temperature of the reaction mixture to about        50° C. to obtain        (−)-trans-1,2-hydroxy-3-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-4,6-dimethoxy-phenyl)-ethanone,        represented by the following Formula G;

-   -    (hereinafter referred to as compound G);    -   (iii) reacting compound G with methyl 2-chlorobenzoate in the        presence of a base and a suitable solvent under an atmosphere of        nitrogen, followed by acid catalysed cyclisation to give        (+)-trans-2-(2-chlorophenyl)-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-5,7-dimethoxy-chromen-4-one        represented by the following Formula 2A;

-   -    (hereinafter referred to as compound 2A);    -   (iv) subjecting compound 2A to demethylation by heating it with        pyridine hydrochloride at a temperature in the range of        120-180° C. to obtain compound 1A; and    -   (v) optionally, converting compound 1A to its pharmaceutically        acceptable salt, such as its hydrochloride salt,        (+)-trans-2-(2-chlorophenyl)-5,7-dihydroxy-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-chromen-4-one        hydrochloride, by conventional means.

The compound (E)-methyl-2-nitro-3-(2,4,6-trimethoxyphenyl)acrylate usedin step (a) may be prepared by a reaction between2,4,6-trimethoxybenzaldehyde and methyl nitroacetate in the presence ofammonium acetate and magnesium sulphate. The compound,2,4,6-trimethoxybenzaldehyde can be prepared by conventional methodsfrom 2,4,6-trimethoxybenzene by reaction with phosphoryl chloride andN,N-dimethylformamide. The compound methyl nitroacetate can be preparedfrom nitromethane by conventional methods, for instance, heatingnitromethane with a base, for example, potassium hydroxide, at 160° C.followed by treatment at 15° C. with sulphuric acid and methanol.

The catalyst complex used in step (a) above comprises a chiralbis(oxazoline) ligand and a metal complex. The use of chiralbis(oxazoline) ligands in catalytic asymmetric synthesis have beenextensively reported (Ghosh, A. K.; Mathivanan, P.; Cappiello, J.Tetrahedron: Asymmetry 1998, 9, 1-45). According to the presentinvention, the preferred chiral bis(oxazoline) ligand is(3aS,3a′S,8aR,8a′R)-2,2′(cyclopropane-1,1-diyl)bis(8,8a-dihydro-3aH-indeno[1,2d]oxazole)which can be prepared as per the method reported in J. Am. Chem. Soc.2002, 124(44), 13097-13105, which is incorporated herein by reference.The reaction can be carried out using only 4 to 6 mol % chiralbis(oxazoline) ligand.

Metal complexes suitable for providing a catalyst complex includemagnesium trifluoromethanesulphonate, magnesium perchlorate, coppertrifluoromethanesulphonate, zinc trifluoromethanesulphonate, lanthanumtrifluoromethanesulphonate, nickel trifluoromethanesulphonate, magnesiumbromide, copper bromide, zinc bromide, nickel bromide, magnesium iodide,copper iodide, zinc iodide, nickel iodide, magnesium acetylacetonate,copper acetylacetonate, zinc acetylacetonate, and nickelacetylacetonate. According to the present invention, the preferred metalcomplex is magnesium trifluoromethanesulphonate.

The base used in step (a) may be selected from: triethylamine,diisopropylamine, 2,6-lutidine, N-methylmorpholine, N-ethylpiperidine,imidazole and 5,6-dimethylbenzimidazole. Preferably, N-methylmorpholineis used as the base.

The reducing agent as used in step (b) may be stannous chloride or Raneynickel. When stannous chloride is used as the reducing agent, compound Cis obtained as a single isomer. When Raney nickel is used as thereducing agent, compound C is obtained as a mixture of isomers, asindicated by ¹H NMR. If a small sample of the mixture of isomers ispurified by column chromatography to separate the isomers, it can beconfirmed that one of the isomers is identical to the single isomerobtained using stannous chloride as the reducing agent. The solvent usedin step (b) is preferably an aprotic solvent, such as ethyl acetate,dioxane, N,N-dimethylformamide and tetrahydrofuran. When reduction iscarried out with stannous chloride, the solvent used is preferably ethylacetate, and when reduction is carried out with Raney nickel, thesolvent used is preferably selected from: tetrahydrofuran, dioxane andN,N-dimethylformamide.

The solvent used in the decarboxylation step (c) is preferably a polaraprotic solvent such as N-methylpyrrolidone and dimethyl sulphoxide.

The methylating agent used in step (d) may be methyl iodide or dimethylsulphate. The solvent used in step (d) is preferably a polar aproticsolvent which may be selected from: N,N-dimethylformamide,tetrahydrofuran and dioxane. The alkaline metal carbonate may be sodiumcarbonate or potassium carbonate. The alkaline metal hydride may besodium hydride. The alkaline metal hydroxide may be sodium hydroxide orpotassium hydroxide. The alcohol used is preferably an acyclic alcohol.More preferably, the alcohol is selected from: ethanol, methanol andisopropanol.

The reducing agent used in step (e) is preferably a hydride, morepreferably a hydride selected from: lithium aluminium hydride,diisobutyl aluminium hydride and sodium borohydride. The solvent used inthe reduction step is preferably an ether. More preferably the solventis selected from: tetrahydrofuran, dioxane and diethyl ether.

In the process for the preparation of compounds of Formula 1 from theintermediate compounds of Formula A, the catalyst used in step (i) maybe selected from a Lewis acid and polyphosphoric acid. The Lewis acidcatalyst may be selected from zinc chloride, aluminium chloride, borontrifluoride and boron tribromide. The most preferred Lewis acid catalystis boron trifluoride.

The alkali used in step (ii) may be sodium hydroxide or potassiumhydroxide.

The base used in step (iii) may be selected from: sodium hydride,n-butyl lithium, lithium hexamethyldisilazide and lithiumdiisopropylamide. The base used is preferably sodium hydride. Thesolvent used in step (iii) may be selected from: tetrahydrofuran,N,N-dimethylformamide and dioxane. The solvent used is preferablyN,N-dimethylformamide.

The demethylating agent used in step (iv) may be selected from pyridinehydrochloride, boron tribromide, boron trifluoride etherate andaluminium trichloride. The preferred demethylating agent is pyridinehydrochloride.

Thus, according to the process of the present invention, the compound ofFormula A is obtained with a chiral purity of greater than 97% ee(enantiomeric excess) leading to the compounds of Formula 1 with achiral purity of greater than 99% ee.

The compounds of Formula 1 obtained by the novel process of the presentinvention may be optionally converted to their correspondingpharmaceutically or toxicologically acceptable salts, in particulartheir pharmaceutically utilizable salts.

Compounds of Formula 1 which contain one or more basic groups, i.e.groups which can be protonated can be used according to the invention inthe form of their addition salts with non-toxic inorganic or organicacids. Examples of suitable inorganic acids include: boric acid,perchloric acid, hydrochloric acid, hydrobromic acid, sulfuric acid,sulphamic acid, phosphoric acid, nitric acid and other inorganic acidsknown to the person skilled in the art. Examples of suitable organicacids include: acetic acid, gluconic acid, propionic acid, succinicacid, glycolic acid, stearic acid, lactic acid, malic acid, tartaricacid, citric acid, ascorbic acid, pamoic acid, maleic acid,hydroxymaleic acid, phenylacetic acid, glutamic acid, benzoic acid,salicylic acid, sulphanilic acid, 2-acetoxybenzoic acid, fumaric acid,toluenesulphonic acid, methanesulphonic acid, ethanedisulphonic acid,oxalic acid, isethionic acid, ketoglutaric acid, benzenesulphonic acid,glycerophosphoric acid and other organic acids known to the personskilled in the art. The compounds of Formula 1, which contain acidicgroups can be used according to the invention, for example, as alkalimetal salts like Li, Na, and K salts. The pharmaceutically acceptablesalts of the present invention can be synthesized from the subjectcompound, which contains basic and acidic moieties, by conventionalchemical methods. Generally, the salts are prepared by contacting thefree base or acid with stoichiometric amounts or with an excess of thedesired salt-forming inorganic or organic acid or base in a suitablesolvent or dispersant or by anion exchange or cation exchange with othersalts. Suitable solvents are, for example, ethyl acetate, ether,alcohols, acetone, tetrahydrofuran, dioxane or mixtures of thesesolvents.

It is understood that modifications in reaction conditions that do notaffect the chirality of the various embodiments of this invention areincluded within the invention disclosed herein. Accordingly, thefollowing examples are intended to illustrate but not to limit thepresent invention.

EXAMPLES Example 1 (E)-Methyl-2-nitro-3-(2,4,6-trimethoxyphenyl)acrylate

2,4,6-trimethoxybenzaldehyde (20.75 g, 0.105 mol) was dissolved indichloromethane (300 mL) and to this solution magnesium sulphate (15 g,0.124 mol), ammonium acetate (10 g, 0.129 mol) and methyl nitroacetate(12.60 g, 0.105 mol) were added and stirred at room temperature for 2hours. At the end of two hours, water (300 mL) was added to the reactionmass, the organic layer was separated and the aqueous layer extractedwith dichloromethane (2×100 mL). The organic layers were combined andconcentrated under reduced pressure to give a solid, which wascrystallized from methanol (100 mL).

Yield: 22 g (66.82%) ¹H NMR (CDCl₃): δ 8.37 (s, 1H), 6.08 (s, 2H), 3.86(s, 3H), 3.84 (s, 3H), 3.82 (s, 6H). MS (ES+): 298 (M+1)

Example 2 (+)-Trimethyl3-nitro-2-(2,4,6-trimethoxyphenyl)propane-1,1,3-tricarboxylate

In a two-necked 500 mL round-bottomed flask maintained under nitrogen,chloroform (10 mL), magnesium triflate (0.161 g, 0.5 mmol) and water(0.036 mL, 2.0 mmol) were added. To this stirred solution,(3aS,3a′S,8aR,8a′R)-2,2′(cyclopropane-1,1-diyl)bis(8,8a-dihydro-3aH-indeno[1,2-d]oxazole)(bis(oxazoline)) (0.196 g, 0.55 mmol) was added and the reaction mixturestirred for 1 hour. At the end of 1 hour, chloroform (30 mL) andmolecular sieves (2 g) were added and the mixture stirred for another 90mins. (E)-Methyl-2-nitro-3-(2,4,6-trimethoxyphenyl)acrylate (3.1 g, 0.01mol), dimethyl malonate (1.92 g, 0.014 mol) and N-methylmorpholine (0.06g, 0.6 mmol) were added and the reaction mixture was stirred for 12hours followed by heating at 40° C. for 4 hours. Petroleum ether (15 mL)was added to the reaction mixture, stirred for 10 mins. and the mixturefiltered. The molecular sieves were washed with methyl-t-butyl ether andthe combined organic layer was washed with 5% phosphoric acid (10 mL)and brine (15 mL). The organic layer was concentrated under reducedpressure to give an oil. The oil was dissolved in methanol (10 mL),cooled and filtered to give a white crystalline solid.

Yield: 2.9 g (67.82%) ¹H NMR (CDCl₃): δ (6.05 (br.s, 1H), 6.03 (br.s,1H), 6.0 (d, 1H, 12.0 Hz), 5.24 (dd, 1H, 9.0 Hz, 12.0 Hz), 4.26 (d, 1H,9.0 Hz), 3.83 (s, 6H), 3.77 (s, 3H), 3.76 (s, 3H), 3.72 (s, 3H), 3.4 (s,3H). MS (ES+): 430 (M+1)

Example 3 (+)-Dimethyl5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2,4-dicarboxylate

Method 1

(+)-Trimethyl3-nitro-2-(2,4,6-trimethoxyphenyl)propane-1,1,3-tricarboxylate (7.8 g,0.018 mol) was dissolved in ethyl acetate (100 mL). To this solution,stannous chloride dihydrate (25 g, 0.118 mol) was added in portions overa period of 10 mins under stirring. The reaction mixture was heated to55° C. for 2 hours. The mixture was cooled to 10° C., basified with 10%sodium hydroxide solution to pH 9, filtered through a celite pad and thepad washed with ethyl acetate (50 mL). The aqueous layer was extractedwith ethyl acetate (2×100 mL). The organic layers were combined, driedover anhydrous sodium sulphate and concentrated under reduced pressureto give the title compound as a white solid.

Yield: 4.5 g (67.44%) ¹H NMR (CDCl₃): δ 6.06 (br.s, 2H), 6.00 (br.s,1H), 4.98 (dd, 1H), 4.59 (d, 1H), 3.96 (d, 1H), 3.79 (s, 3H), 3.76 (s,9H), 3.35 (s, 3H). MS (ES+): 368 (M+1)

Method 2

To a 1 L pressure reactor, tetrahydrofuran (100 mL) and Raney nickel (20g) was added followed by the addition of a solution of (+)-trimethyl3-nitro-2-(2,4,6-trimethoxyphenyl)propane-1,1,3-tricarboxylate (32 g,0.074 mol) in tetrahydrofuran (300 mL). Under stirring, the reactor waspurged three times with nitrogen followed by hydrogen. The reactionmixture was stirred overnight under a hydrogen pressure of 80 psi. Atthe end of the reaction, Raney nickel was filtered off and washed withtetrahydrofuran (150 mL) under nitrogen. The organic layer wasconcentrated under reduced pressure to yield a white solid. ¹H NMRrevealed the presence of a mixture of isomers. The mixture of cis andtrans isomers was obtained in a yield of 25 g (91.32%). A small portionof reaction mixture was purified by column chromatography using 5%methanol in chloroform as eluting agent to separate the isomers and oneof the separated isomers was found to be identical to the isomerobtained by reduction using stannous chloride, confirmed by ¹H NMR, massspectra and HPLC.

¹H NMR (CDCl₃): δ 6.06 (br.s, 2H), 6.00 (br.s, 1H), 4.98 (dd, 1H), 4.59(d, 1H), 3.96 (d, 1H), 3.79 (s, 3H), 3.76 (s, 9H), 3.35 (s, 3H). MS(ES+): 368 (M+1)

Example 4 (+)-Methyl5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate

(+)-Dimethyl5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2,4-dicarboxylate (4.0 g,0.0109 mol) was dissolved in N-methylpyrrolidone (15 mL). Sodiumchloride (0.631 g, 0.0109 mol) and water (0.196 mL, 0.0109 mol) wereadded and the reaction mixture was heated to 170° C. for 5 hours. Thereaction mixture was poured on ice (50 g) and the solid was filtered anddried.

Yield: 1.5 g (44.5%)

The product was a mixture of cis and trans isomers as seen in the ¹HNMR. The mixture of the isomers was used without separation for furtherreaction. A small amount of the mixture was purified by columnchromatography (5% methanol in chloroform) for spectral characterizationof the cis and trans isomers.

(+)-cis-Methyl 5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate

¹H NMR (CDCl₃): δ 6.08 (s, 2H), 5.89 (br.s, 1H), 4.62 (m, 1H), 4.48 (d,1H, 9.6 Hz), 3.79 (s, 3H), 3.76 (s, 6H), 3.34 (s, 3H), 2.74 (dd, 1H),2.60 (dd, 1H). MS (ES+): 310 (M+1)

(+)-trans-Methyl5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate

¹H NMR (CDCl₃): δ 6.15 (s, 2H), 5.87 (br.s, 1H), 4.42 (d, 1H, 7.5 Hz),4.26 (m, 1H), 3.82 (s, 3H), 3.81 (s, 6H), 3.68 (s, 3H), 2.76 (dd, 1H),2.53 (dd, 1H). MS (ES+): 310 (M+1)

Example 5 (+)-Methyl-1-methyl-5-oxo-3-(2,4,6trimethoxyphenyl)pyrrolidine-2-carboxylate

(+)-Methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate(1.7 g, 0.0055 mol) was dissolved in N,N-dimethylformamide (15 mL) andthe solution cooled to 0° C. Sodium hydride (0.134 g, 0.0056 mmol) wasadded in portions over a period of 10 minutes and stirred for another 20minutes at 0° C. Methyl iodide (0.514 mL, 0.0082 mol) was added dropwiseand the reaction allowed to warm to room temperature in 1 hour. Thereaction mixture was poured slowly over a mixture of crushed ice (20 g)and 1:1 hydrochloric acid solution (5 mL). The mixture was extractedwith ethyl acetate (2×50 mL), washed with brine, dried over anhydroussodium sulphate and concentrated under reduced pressure to yield an oil.The oil was triturated with petroleum ether and the resulting solid wasfiltered.

Yield: 1.7 g (96.04%)

The product was a mixture of cis and trans isomers as seen in the ¹HNMR. The mixture of the isomers was used without separation for furtherreaction. A small amount of the mixture was purified by columnchromatography (5% methanol in chloroform) for spectral characterizationof the cis and trans isomers.

(+)-cis-methyl1-methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate

¹H NMR (CDCl₃): δ 6.07 (s, 2H), 4.44 (dd, 1H), 4.27 (d, 1H, 9.6 Hz),3.79 (s, 3H), 3.74 (s, 6H), 3.38 (s, 3H), 3.20 (dd, 1H), 2.90 (s, 3H),2.45 (dd, 1H) MS (ES+): 324 (M+1)

(+)-trans-Methyl-1-methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate

¹H NMR (CDCl₃): δ 6.12 (s, 2H), 4.13 (d, 1H, 6.3 Hz), 4.05 (dd, 1H),3.80 (s, 3H), 3.76 (s, 6H), 3.70 (s, 3H), 2.88 (s, 3H), 2.64 (m, 2H). MS(ES+): 324 (M+1)

Example 6(−)-trans-1-Methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylicacid

The mixture of cis and trans isomers ofmethyl-1-methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate(1.6 g, 0.0049 mol) was dissolved in methanol (15 mL). To this, asolution of potassium hydroxide (0.96 g, 0.017 mol) in water (4 mL) wasadded and the reaction mixture heated at 65° C. for 3 hours. Methanolwas removed under reduced pressure, 15 mL water was added and themixture acidified with 1:1 hydrochloric acid solution to pH 2. Theresulting solid was filtered, washed with water and dried.

Yield: 0.94 g (61.44%) ¹H NMR (CDCl₃): δ 6.13 (s, 2H), 4.16 (m, 2H),3.80 (S, 3H), 3.77 (S, 6H), 2.93 (S, 3H), 2.74 (m, 1H), 2.62 (m, 1H). MS(ES+); 310 (M+1) [α]_(D) ²⁵: −37.83° (c=0.518, MeOH)

Example 7(−)-trans-(1-methyl-3-(2,4,6-trimethoxyphenyl)pyrrolidin-2-yl)methanol

Lithium aluminum hydride (0.304 g, 0.008 mol) was stirred intetrahydrofuran (40 mL) under a nitrogen atmosphere.(−)-trans-1-Methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylicacid (1.0 g, 0.0032 mol) was added in portions and the reaction mixturewas stirred with heating at 50° C. for 90 minutes. The reaction mixturewas cooled to 10° C. and diluted with water (2.5 mL) and 15% sodiumhydroxide solution (0.6 mL) under stirring. The solid was filtered andwashed with ethyl acetate (10 mL). The organic layers were combined andconcentrated under reduced pressure to give a white solid.

Yield: 0.91 g (100%) ¹H NMR (CDCl₃): δ 6.16 (s, 2H), 3.98 (m, 1H), 3.64(s, 9H), 3.62 (dd, 1H), 3.43 (d, 1H), 3.21 (m, 1H), 2.78 (m, 1H), 2.63(m, 1H), 2.44 (s, 3H), 2.04 (m, 2H) MS (ES+): 282 (M+1) [α]_(D) ²⁵: −20°(c=0.2, MeOH)

Example 8 (−)-trans-Acetic acid3-(3-acetyl-2-hydroxy-4,6-dimethoxy-phenyl)-1-methyl-pyrrolidin-2-ylmethyl ester

Boron trifluoride diethyl etherate (25.2 g, 0.178 mol) was addeddropwise, with stirring, at 0° C., under a nitrogen atmosphere to asolution of(−)-trans-(1-methyl-3-(2,4,6-trimethoxyphenyl)pyrrolidin-2-yl)methanol(10 g, 0.0356 mol) in acetic anhydride (18 g, 0.178 mol). The reactionmixture was stirred at room temperature for 2 h. It was poured overcrushed ice (1 kg), basified using a saturated aqueous sodium carbonatesolution and extracted using ethyl acetate (3×200 mL). The organicextract was washed with brine, dried (anhydrous sodium sulphate) andconcentrated to get title compound.

Yield: 10 g (80%) ¹H NMR (CDCl₃): δ 14.20 (s, 1H), 5.96 (s, 1H), 4.10(d, 2H), 3.90 (s, 3H), 3.89 (s, 3H), 3.85 (m, 1H), 3.26 (m, 1H), 2.82(m, 1H), 2.74 (m, 1H), 2.66 (s, 3H), 2.52 (s, 3H), 2.21 (m, 2H), 2.10(s, 3H).

Example 9(−)-trans-[2-Hydroxy-3-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-4,6-dimethoxy-phenyl)-ethanone

To a solution of (−)-trans-aceticacid-3-(3-acetyl-2-hydroxy-4,6-dimethoxy-phenyl)-1-methyl-pyrrolidin-2-ylmethyl ester) (10 g, 0.0284 mol) in methanol (25 mL) was added withstirring, at room temperature, a 10% aqueous sodium hydroxide (25 mL)solution. The temperature of the reaction mixture was raised to 50° C.for 45 minutes, cooled to room temperature, acidified using 1:1hydrochloric acid solution and concentrated to remove methanol. It wasbasified using a saturated aqueous sodium carbonate solution. Theprecipitated compound was filtered, washed with water and dried.

Yield: 7.14 g (81.1%) IR (KBr): 3400, 3121, 3001, 1629, 1590 cm⁻¹. ¹HNMR (CDCl₃): δ 5.96 (s, 1H), 3.93 (m, 1H), 3.90 (s 3H), 3.88 (s, 3H),3.59 (dd, 1H), 3.37 (d, 1H), 3.13 (m, 1H), 2.75 (m, 1H), 2.61 (s, 3H),2.59 (m, 1H), 2.37 (s, 3H), 2.00 (m, 2H). MS (ES+): m/z 310 (M+1)

Example 10(+)-trans-2-(2-Chlorophenyl)-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-5,7-dimethoxy-chromen-4-one

Sodium hydride (50%, 0.54 g, 0.01125 mol) was added in portions to asolution of (−)-trans-acetic acid3-(3-acetyl-2-hydroxy-4,6-dimethoxy-phenyl)-1-methyl-pyrrolidin-2-ylmethyl ester (0.7 g, 0.0022 mol) in N,N-dimethylformamide (15 mL) at 0°C., under a nitrogen atmosphere and with stirring. After 10 minutes,methyl 2-chlorobenzoate (1.15 g, 0.00675 mol) was added. The reactionmixture was stirred at 25° C. for 2 h. Methanol was added carefullybelow 20° C. The reaction mixture was poured over crushed ice (300 g),acidified with 1:1 hydrochloric acid solution to pH 2 and extractedusing ethyl acetate (2×100 mL). The aqueous layer was basified using asaturated sodium carbonate solution to pH 10 and extracted usingchloroform (3×200 mL). The organic layer was dried over anhydrous sodiumsulphate and concentrated. To the residue, concentrated hydrochloricacid (25 mL) was added and stirred at room temperature for 2 h. Thereaction mixture was poured over crushed ice (300 g) and made basicusing a saturated sodium carbonate solution. The mixture was extractedusing chloroform (3×200 mL). The organic extract was washed with water,dried over anhydrous sodium sulphate and concentrated to obtain thetitle compound.

Yield: 0.67 g (68.88%) mp: 95-97° C. IR (KBr): 3400, 1660 cm⁻¹. [α]_(D)²⁵=+5.8° (c=0.7, methanol) ¹H NMR (CDCl₃): δ 7.7 (dd, 1H), 7.41 (m, 1H),7.45 (m, 2H), 6.55 (s, 1H), 6.45 (s, 1H), 4.17 (m, 1H), 4.05 (s, 3H),3.95 (s, 3H), 3.65 (dd, 1H), 3.37 (dd, 1H), 3.15 (m, 1H), 2.77 (d, 1H),2.5 (m, 1H), 2.3 (s, 3H), 2.05 (m, 2H). MS: m/e 430 (M⁺), 398 (M−31)

Example 11(+)-trans-2-(2-Chlorophenyl)-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-5,7-dihydroxy-chromen-4-one

Molten pyridine hydrochloride (4.1 g, 0.0354 mol) was added to(+)-trans-2-(2-chlorophenyl)-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-5,7-dimethoxy-chromen-4-one(0.4 g, 0.0009 mol) and heated at 180° C. for 1.5 h. The reactionmixture was cooled to 25° C., diluted with methanol (10 mL) and basifiedusing sodium carbonate to pH 10. The mixture was filtered and theorganic layer was concentrated. The residue was suspended in water (5mL), stirred for 30 minutes, filtered and dried to obtain the titlecompound.

Yield: 0.25 g (66.86%) IR (KBr): 3422, 3135, 1664, 1623, 1559 cm⁻¹. ¹HNMR (CDCl₃): δ 7.56 (d, 1H), 7.36 (m, 3H), 6.36 (s, 1H), 6.20 (s, 1H),4.02 (m, 1H), 3.70 (m, 2H), 3.15 (m, 2H), 2.88 (m, 1H), 2.58 (s, 3H),2.35 (m, 1H), 1.88 (m, 1H). MS (ES+): m/z 402 (M+1) Analysis:C₂₁H₂₀ClNO₅C, 62.24 (62.71); H, 5.07 (4.97); N, 3.60 (3.48); Cl, 9.01(8.83).

Example 12(+)-trans-2-(2-Chloro-phenyl)-5,7-dihydroxy-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-chromen-4-onehydrochloride

(+)-trans-2-(2-Chlorophenyl)-8-(2-hydroxymethyl-1-methyl-pyrrolidin-3-yl)-5,7-dimethoxy-chromen-4-one(0.2 g, 0.48 mmol) was suspended in methanol (2 mL) and ethereal HCl (5mL) was added. The suspension was stirred to get a clear solution. Thesolution was concentrated under reduced pressure to obtain the titlecompound.

Yield: 0.21 g (97%) [α]_(D) ²⁵=+21.2° (c=0.2, methanol) ¹H NMR (CD₃OD,300 MHz): δ 7.80 (d, 1H), 7.60 (m, 3H), 6.53 (s, 1H), 6.37 (s, 1H), 4.23(m, 1H), 3.89 (m, 2H), 3.63 (m, 1H), 3.59 (dd, 1H), 3.38 (m, 1H), 2.90(s, 3H), 2.45 (m, 1H), 2.35 (m, 1H). MS (ES+): m/z 402 (M+1), free base.

1. A process for the preparation of the compound (−)-trans-(1-methyl-3-(2,4,6-trimethoxyphenyl)pyrrolidin-2-yl)-methanol represented by Formula A;

comprising treating the compound (−)-trans-1-methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylic acid of the following Formula E;

(hereinafter referred to as compound E), with a reducing agent in a solvent.
 2. The process according to claim 1, wherein the reducing agent is a hydride.
 3. The process according to claim 2, wherein the hydride is selected from lithium aluminium hydride, diisobutyl aluminium hydride and sodium borohydride.
 4. The process according to claim 1, wherein the solvent used is an ether.
 5. The process according to claim 4, wherein the ether is selected from tetrahydrofuran, dioxane and diethyl ether.
 6. The process according to claim 1, wherein the compound E is prepared by (a) carrying out a stereospecific Michael addition of dimethyl malonate to (E)-methyl-2-nitro-3-(2,4,6-trimethoxyphenyl)acrylate in a solvent in the presence of a catalyst complex, a base and molecular sieves, wherein the catalyst complex comprises a chiral bis(oxazoline) ligand and a metal complex, to obtain (+)-trimethyl-3-nitro-2-(2,4,6-trimethoxyphenyl) propane-1,1,3-tricarboxylate represented by the following Formula B;

(hereinafter referred to as compound B); (b) treating compound B as obtained in step (a) with a reducing agent in a solvent to obtain (+)-dimethyl-5-oxo-3-(2,4,6-trimethoxyphenyl)-pyrrolidine-2,4-dicarboxylate represented by the following Formula C;

(hereinafter referred to as compound C); (c) treating compound C with sodium chloride in a solvent and heating the resulting reaction mixture to a temperature in the range of 120° C. to 170° C. to obtain (+)-methyl-5-oxo-3-(2,4,6-trimethoxyphenyl)pyrrolidine-2-carboxylate as a mixture of cis and trans isomers, represented by the following Formula D;

(hereinafter referred to as compound D); (d) reacting compound D with a methylating agent in a solvent and a base selected from an alkaline metal hydride and an alkaline metal carbonate; followed by subjecting the resulting mixture of cis and trans compounds to alkaline hydrolysis with an alkaline metal hydroxide in an alcohol, and heating the resulting reaction mixture to a temperature in the range of 50° C. to 100° C. to obtain compound E as a single trans isomer.
 7. The process according to claim 6, wherein the chiral bis(oxazoline) ligand used in step (a) is (3aS,3a′S,8aR,8a′R)-2,2′(cyclopropane-1,1-diyl)bis(8,8a-dihydro-3aH-indeno[1,2d]oxazole).
 8. The process according to claim 6, wherein the metal complex used in step (a) is selected from magnesium trifluoromethanesulphonate, magnesium perchlorate, copper trifluoromethanesulphonate, zinc trifluoromethanesulphonate, lanthanum trifluoromethanesulphonate, nickel trifluoromethanesulphonate, magnesium bromide, copper bromide, zinc bromide, nickel bromide, magnesium iodide, copper iodide, zinc iodide, nickel iodide, magnesium acetylacetonate, copper acetylacetonate, zinc acetylacetonate, and nickel acetylacetonate.
 9. The process according to claim 8, wherein the metal complex is magnesium trifluoromethanesulphonate.
 10. The process according to claim 6, wherein the base used in step (a) is selected from triethylamine, diisopropylamine, 2,6-lutidine, N-methylmorpholine, N-ethylpiperidine, imidazole and 5,6-dimethylbenzimidazole.
 11. The process according to claim 10, wherein the base is N-methylmorpholine.
 12. The process according to claim 6, wherein in step (b), the treatment of compound B with a reducing agent in a solvent is carried out using stannous chloride as the reducing agent.
 13. The process according to claim 12, wherein the solvent is ethyl acetate.
 14. The process according to claim 6, wherein in step (b), the treatment of compound B with a reducing agent in a solvent is carried out using Raney nickel as the reducing agent.
 15. The process according to claim 14, wherein the solvent is selected from tetrahydrofuran, dioxane and N,N-dimethylformamide. 